For example, when replacing an air conditioner installed in a building or the like with another model, it is typical to replace only a refrigerant and reuse an existing refrigerant piping between an outdoor unit and an indoor unit as-is for reasons such as cutting costs. In this case, if the amount of replaced refrigerant is greater or less than the correct amount, there is a risk of falling into an uncooled state in which the required cooling capacity is no longer ensured. Consequently, when replacing a refrigerant, it is necessary to fill in a suitable amount of the refrigerant according to the length of the refrigerant piping (refrigerant piping length).
However, the refrigerant piping is sometimes laid out in a different arrangement than design specifications due to construction problems or other issues, and there is no guarantee that the actual refrigerant piping length necessarily matches the values stated in the design specifications.
Accordingly, Patent Literature 1, for example, proposes technology that attaches a transmitter, which imparts vibrations to refrigerant piping, and multiple receivers, which detect the vibrations, at given positions along the refrigerant piping, measures the length of each segment from the propagation time by which each receiver detects the vibrations imparted by the transmitter, and computes the refrigerant piping length on the basis of a given algorithm.